How to make the fabric flame retardant?

All fabrics will burn,  but some are more combustible than others.  

Untreated natural fibers such as cotton, linen and silk burn more readily than wool, which is more difficult to ignite and burns with a low flame velocity.

The weight and weave of the fabric will affect how easily the material will ignite and burn.

Fabrics with a tight weave - wool, modacrylic, 100 percent polyester and those that are flame-retardant treated are good choices. Heavy, tight weave fabrics will burn more slowly than loose weave, light fabrics of the same material. The surface texture of the fabric also affects flammability. Fabrics with long, loose, fluffy pile or "brushed" nap will ignite more readily than fabrics with a hard, tight surface, and in some cases will result in flames flashing across the fabric surface.

Most synthetic fabrics, such as nylon, acrylic or polyester resist ignition. However, once ignited, the fabrics melt. This hot, sticky, melted substance causes localized and extremely severe burns. When natural and synthetic fibers are blended, the hazard may increase because the combination of high rate of burning and fabric melting usually will result in serious burns. In some cases, the hazard may be greater than that of either fabric individually.

Curtains, draperies and other articles in the home can have their burning rates reduced with flame retardants applied through chemical treatment. Such flame-retardant treatment after manufacturing is not recommended for clothing.

The design of clothing also may influence the flammability of the garment. Full, long and loose garments tend to ignite easily and have a higher rate of burning since more material is exposed to the atmosphere than with close-fitting garments.

Flame-retardant materials used in garments require special laundering to maintain the flame-retardant effectiveness. Flame-retardant materials should be washed only with standard detergents. Clothing labels usually provide adequate information about the care of the garment.